The effect of partial substitution of in by X = Si, Ge and Al on the crystal structure, magnetic properties and resistivity of Ni₅₀Mn ₃₅In₁₅ Heusler alloys

The effect of partial substitution of In by X = Si, Ge and Al on the structural, electrical and magnetocaloric properties of Ni₅₀Mn ₃₅In₁₅ Heusler alloys was studied using x-ray diffraction, resistivity, magnetization and thermal expansion measurements. It was observed that the presence of X atoms (∼7% X) at In sites strongly affects the crystal structure and electric and magnetic behaviours of Ni₅₀Mn ₃₅In₁₅. Martensitic (Pmmm space group) and austenitic ( ) crystal structures were observed at room temperature for Ni₅₀Mn ₃₅In₁₄Ge, Ni₅₀Mn₃₅In₁₄Al and Ni₅₀Mn₃₅In₁₄Si. All samples were found to show unidirectional anisotropy at low temperatures (T < 150 K). Giant positive and negative magnetic entropy changes, as large as ΔS _M, + 82 J Kg^-1 K^-1 (at T = 274 K) and -6.6 J Kg^-1 K^-1 (at T = 307 K) were found for a magnetic field change of 5 T with X = Si. The net refrigeration capacity was also observed to change significantly. The maximum negative magnetoresistance was found to be 50% for Ni₅₀Mn₃₅In₁₄Si at H = 5 T and T = 284 K. Phase transition temperatures attributed to martensitic transformation and to ferromagnetic ordering in martensitic and austenitic phases were determined. The influence of the interatomic distance on the properties of Ni ₅₀Mn₃₅In₁₅ was discussed.